This invention relates generally to hydraulically driven mowing machines or mowers and more particularly to large roadside mowers of the type propelled or pulled by a tractor or other vehicle.
The use of hydraulic motors to power mowing machines or other implements is known in the art. Examples of mowing machines which have hydraulically driven cutting means are found in the following U.S. Patents:
U.S. Pat. No. 2,166,940--C. M. Conradson PA0 U.S. Pat. No. 2,603,052--C. L. Pelham PA0 U.S. Pat. No. 2,840,974--T. J. Dunn Et Al PA0 U.S. Pat. No. 2,888,088--A. Claas Et Al PA0 U.S. Pat. No. 3,087,296--J. T. Cowles PA0 U.S. Pat. No. 3,135,079--T. J. Dunn PA0 U.S. Pat. No. 3,221,482--R. E. Cowling PA0 U.S. Pat. No. 3,263,036--R. W. Bailey Et Al PA0 U.S. Pat. No. 3,319,407--B. L. Jordan Et Al PA0 U.S. Pat. No. 3,404,518--H. D. Kasper PA0 U.S. Pat. No. 3,462,925--J. K. Lanier PA0 U.S. Pat. No. 3,498,036--R. E. Cowling Et Al PA0 U.S. Pat. No. 3,511,033--R. K. Strasel PA0 U.S. Pat. No. 3,526,083--R. O. Barry Et Al PA0 U.S. Pat. No. 3,563,012--R. K. Strasel PA0 U.S. Pat. No. 3,727,712--M. J. Colloton PA0 U.S. Pat. No. 3,788,418--Clancey Et Al PA0 U.S. Pat. No. 3,832,835--Hall Et Al PA0 U.S. Pat. No. 3,854,271--E. J. Aldred PA0 U.S. Pat. No. 3,949,539--J. O. Cartner PA0 U.S. Pat. No. 3,973,379--F. A. Ecker Et Al.
In particular, in U.S. Pat. Nos. 2,603,052 and 2,840,974 there are shown hydraulically powered sickle mowing machines. In U.S. Pat. No. 3,511,033, there is shown a rotary reel-type mowing machine which is hydraulically-powered. There are many examples of hydraulically-powered rotary mowing machines such as that shown in U.S. Pat. No. 3,135,079.
The use of hydraulic power has particular utility for multiple unit mowing machines as well as for side mounted and boom mounted mowing machines when the drive-train is not readily suited for a mechanical drive. Mowers such as shown in U.S. Pat. No. 3,404,518 and the enclosed brochure depicting the "TK-15" fifteen foot rotary mower of assignee Terrain King Corporation of Seguin, Texas generally require folding wing sections for transport. U.S. Pat. No. 3,404,518 attempts to solve the transporting problem of multiple gang mowers by having only the outer housing sections foldably mounted. In the case of the "TK-15" mower by Terrain King Corporation, the entire outer wing section folds for transport purposes. In the case of typical shaft driven sections, provision must be made for the folding.
It is desirable to eliminate the mechanical drive train of mowing machines since they can become quite complicated when multiple mowing units are provided. However, in the case of hydraulical motors, the efficiency of the motors and the heat generated in the hydraulic drive fluid may be a problem. Conventional hydraulic piston pumps and motors may be used on mowers because of their high efficiency. Gear-type pumps and motors are advantageous since they can be more easily controlled in the case of dividing flow for multiple motors.
A problem with large motors of the type shown in U.S. Pat. No. 3,135,079 is the heat generated in hydraulic drive fluid. Under heavy load conditions the hydraulic drive fluid may reach such a high operating temperatures that it can be damaged. Accordingly, some way must be provided to cool the hydraulic fluid to dissipate the heat created by the high pressure pumps and motors utilized. Increasing the amount of hydraulic fluid may help cooling. However, this increases the weight of the machine and adds to the cost of operating.
It is known in the prior art that radiators may be utilized to provide cooling to hydraulic fluid. Examples of such cooling devices are found in U.S. Pat. Nos. 2,166,940, 3,727,712 and 3,788,418. These devices use conventional radiators or heat exchangers which in the case of the latter two patents is positioned so that the cooling fan of an engine provides air flow to dissipate the heat. In the case of cooling fins, cuttings may cover or attach to the fins which may reduce their efficiency. It has also been known in the prior art to utilize structural components for conducting and storing hydraulic fluid. An example of this is shown in U.S. Pat. No. 2,888,088 and it is also known to utilize structural members such as in tractor front end fork-lifts and in construction machines and the like to store hydraulic fluid and to act as conduits. The use of frame members for flowing hydraulic fluid has also been known in mowing machines. However, so far as known the only cooling provided by flowing hydraulic fluid through the frame members occurs from radiation or free convection to the surrounding air.
Applicant first discovered that it could obtain adequate and efficient cooling for a hydraulically-driven mowing machine by circulating the return flow of hydraulic fluid through sealed structural members of the deck which members constitute rectangular tubing which forms the skeleton of the mower deck. The mower deck acts as a huge heat sink capable of dissipating the heat generated by the hydraulic system. The tubing and the deck have a continuous, forced flow of air circulating over their lower heat radiating surfaces which is generated by the up-draft-type blades of the mower. This creates a very efficient heat exchange using forced air convection to dissipate the heat with the up-draft blades also acting to suck up vegetation into the cutting plane. The high efficiency minimizes the required hydraulic fluid for cooling which reduces weight.
It was initially thought to be undesirable to utilize the structural members of the mower deck since this requires a special deck for a hydraulic-type mower. For purposes of economy and manufacturing it would be desirable to provide a mower deck which could be used for either a mechanical or a hydraulic-type mowing machine. It was thought that a heat exchanger which was not in the path of air flow of the cutting blades could be utilized. However, such a unit does not have the efficiency of utilizing the air flow from the blades and it is not believed to be as desirable. Not withstanding the increased cost to manufacture the mower deck whose structural members are suitable for flowing low pressure hydraulic fluid, such a device possesses numerous unexpected advantages over other types of cooling means for the hydraulic fluid.
When multiple hydraulic motors have been used it was previously believed that this could be accomplished with a fluid divider. However it has been found that problems arise in designing a fluid divider which will maintain a substantially constant flow of fluid to each motor when very high fluid pressures are involved.
One method used for multiple motors as found in U.S. Pat. No. 3,135,079 which connects the motors in series, and uses a pressure relief valve which bypasses fluid to the sump when the pressure setting is exceeded. In operation if the first motor of such a series overloads then it will dump the hydraulic fluid to the sump which will lessen the amount of fluid supplied to the following motors in the series. This will result in slowing of the following motors which would not be generally desired. Accordingly, it is another object of the invention to provide a hydraulic drive system for multiple hydraulic motors which will maintain a substantially constant flow of fluid to all of the motors when one or more motors experiences excessive loading. Thus all motors operate independent of one another.